There is a considerable market for unsaturated polyester resins with the great majority of the present market comprising spraying an unsaturated polyester resin typically with reinforcing materials, more particularly chopped fiberglass, onto a polyester gel coat in order to provide a fabricated product of high strength. Generally the unsaturated resin composition is sprayed in an open or contact molding process to produce an exterior molded surface formed by a gel coat of the polyester resin, while an additional polyester resin coat is sprayed over the gel coat or more particularly reinforcing fibers such as glass fibers are rolled into the gel coat in the gel condition. Such open molding processes generally are designed to achieve polyester resin cured at ambient or slightly elevated temperatures under little or no pressure. The fabrication of products employing a sprayed, unsaturated polyester resin particularly with reinforcing glass fibers is generally directed to marine use such as the preparation of boat hulls or consumer products such as for example the preparation of tub or shower stalls and other erosion-resistant fabricated products of high strength and light weight.
The polyester resin formulation is generally an unsaturated polyester based resin dissolved in a monomer such as styrene and typically contains an inhibitor to provide shelf life and a catalyst like a peroxide such as methyl ethyl ketone. The unsaturated resin is a condensation polymer prepared by a reaction between an acid and an alcohol. Generally dibasic acids are used such as maleic anhydride or fumaric acid together with the use of neopentyl glycol. The resin is sprayed with reinforcing materials such as fibrous or clay-type particulate materials as reinforcing agents or fillers and more particularly with chopped fiberglass gun roving. For example, a fabricated polyester material may be prepared by spraying the unsaturated polyester resin with the chopped fiberglass gun rovings onto a previously sprayed polyester gel coat with the polyester gel coat forming generally the smooth exterior surface of the fabricated product. After spraying of the polyester resin with the fiberglass, the material in the chopped glass must be rolled in order to saturate the glass into the gel coat and to smooth out the fabricated material. Various promoters such as cobalt salts may be added to the polyester resin in order to speed up reaction times. Such promoters may be used in combination with the methyl ethyl ketone catalyst or other catalyst systems. The process of preparing the unsaturated polyester resin fabricated material is quite slow and very labor intensive. In addition, many of the polyester resin compositions contain styrene as a monomer which is a toxic material; and therefor, the spraying process must be carried out with caution and with adequate safety for the workers.
It is desired to provide for a spray coating to be employed in the place of unsaturated polyester resin spray coatings or in combination therewith, particularly spray coats that may be placed directly over a gel coat with or without the use of reinforcing fibers and wherein the cure times of the resin are reduced, glass roll out is avoided and with a reduction in labor as well as the avoidance of styrene monomeric material.